1. Field of Invention
This invention relates to laser marking devices which apply a laser beam to an object to form marks such as characters and symbols on it, and more particularly a scan type laser marking device.
2. Description of Prior Art
A scan type laser marking device outputs a laser beam in such a manner that the laser beam is applied to the surface of an object such as an article or product while being deflected in a predetermined area in a scanning mode, for instance shown in Unexamined Japanese Patent Publication Sho. 64-11083. In a scan type laser marking device of this type, a conveyor is provided to convey objects successively. In this case, it is necessary to take the speed of the conveyor into consideration to determine the scanning speed; that is, it is necessary to accomplish the marking operation while the object is in the laser beam radiation area. However, it is difficult to set the scanning speed to a suitable value so that the laser beam irradiation time is fully utilized, and the scanning speed is generally higher than required.
If the scanning speed is high as was described above, then the spot of the laser beam is shifted from the aimed position because of a delay in response of the optical system. As a result, patterns such as characters and graphic forms marked on the object are blurred; that is, they are low in picture quality. In addition, the laser beam application time per area is decreased, and therefore it is necessary to increase the output of the laser.
In view of the foregoing, it is preferable to decrease the scanning speed as much as possible; in other words, it is preferable to decrease the scanning speed as much as possible unless a necessary marking operation is adversely affected thereby.
Another laser marking device has a laser source such as for instance a CO.sub.2 laser. Roughly stated, the device operates as follows: The output laser beam of the CO.sub.2 laser is applied to the surface of an object through a scanner made up of a galvano-mirror. Under this condition, the beam deflecting operation of the scanner is controlled with the aid of a computer so that a graphic form is described on the surface of the object.
For instance in the case where, as shown in FIG. 7, it is required to put a predetermined graphic form on an object 181 conveyed by a conveying stand 141 such as a belt conveyer, the conventional laser marking device of this type operates as follows: When the object 181, being conveyed by the conveying stand, comes under a marking head 180, the conveying stand 141 is stopped. Under this condition, the output laser beam of the marking head 180 is deflected both in the direction of X-axis and in the direction of Y-axis while being applied to the surface of the object 181.
In the case of the conventional laser marking device, the object must remain at rest while the mark is being formed on it. Therefore, in the case where it is required to put a pattern on a plurality of objects 181 one after another which are conveyed by the conveying stand 141, it is necessary to stop the conveying stand 141 for every object. This means that the device is low in productive efficiency.